Supporters of a death row inmate scheduled to die Thursday night have petitioned Texas Gov. Rick Perry to intervene in light of the possibility that the convicted killer, Duane Buck, may have been sentenced to die merely on the basis of his race.

On July 30, 1995, Buck, now 46, burst into the home of Debra Gardner, his ex-girlfriend, carrying two loaded rifles. He shot Gardner's friend, Kenneth Butler, and, when she tried to run, chased Gardner down and shot her dead in the street – in front of her two children.

Buck also shot his sister, who was visiting Gardner at the time, but she survived.

Buck never claimed he was innocent. In fact, according to the Austin American-Statesman, when he was arrested, he coldly told police officers that Gardner "got what she deserved."

After being found guilty, Buck's lawyers asked the jury to recommend life in prison without parole; the prosecutors sought the death penalty.

Buck's lawyers called Dr. Walter Quijano, a criminal psychologist, to the stand to assess if Buck posed "future dangerousness" to society – a necessary component of a death sentence conviction.

According to case notes provided by Ray Hill, a Texas activist opposed to the death penalty and host of Execution Watch, a Houston-based radio program about Texas executions, Quijano said Buck had an unhealthy reluctance to let go of past relationships, which could potentially lead to violent behavior.

However, if locked up in prison for the rest of his life, Buck would be unable to form the type of relationships that led him to commit murder, Quijano said, leading him to tell jurors that coupled with the fact Buck had no previous history of violence, he was not a "future danger."

But when prosecutors cross-examined Quijano, they asked if "the race factor, black, increases the future dangerousness for various complicated reasons; is that correct?"

"Yes," Quijano replied.

That was the last time race was mentioned, according to the case notes, but Buck's supporters say that because the prosecutors' question was posed in a racially charged way – using the exact term that must be used to affirm a death penalty conviction – it was enough for jurors to decide that because Buck is black, he posed a future danger to society, despite the alterative of being locked up for the rest of his life.

In closing arguments, the prosecutors reiterated Dr. Quijano’s theory on race and violence when they said to the jury that Dr. Quijano, "who had a lot of experience in the Texas Department of Corrections, . . .told you that there was a probability that [Buck] would commit future acts of violence," despite Dr. Quijano’s testimony arguing the opposite.

"The jury has the right to sort out what they think is important," Hill told The Christian Post. "But apparently, on cross-examination, [Buck] just appeared worse and worse."

Buck’s case was not the first time Quijano had controversially used race as a factor in his testimony.

Texas state attorneys admitted to the U.S. Supreme Court that Quijano’s racial comments were used in the sentencing hearings for six other Texas death row inmates.

"It is inappropriate to allow race to be considered as a factor in our criminal justice system," then-Texas Atty. Gen. John Cornyn said in 2000. "The people of Texas want and deserve a system that affords the same fairness to everyone."

All six of those inmates have been given new sentencing hearings. Buck has not.

Former prosecutors in Buck's case have called on Texas authorities to grant a new sentence hearing.

"Mr. Buck committed a terrible crime, and he must be punished," said Linda Geffin, a former Harris County assistant district attorney, to the Los Angeles Times. But, she added, "I felt compelled to step forward" because of "the improper injection of race in the sentencing hearing in Mr. Buck's case."

According to Mother Jones, Geffin also wrote a letter last week to Governor Rick Perry and the Texas Board of Pardons and Paroles asking them to intervene in the case.

"No individual should be executed without being afforded a fair trial, untainted by considerations of race," she wrote.

Rev. Wayne Whiteside of Crestview Baptist Church, has known Buck for seven years during his prison stay, and says the convicted murderer has changed, according to the Houston Chronicle.

"[Buck] is the most strikingly changed individual that I have encountered in my ministry,” Rev. Whiteside wrote in the clemency petition. “(He) embodies God's power to transform."

On Monday, the Texas Board of Pardons and Paroles rejected Buck's petition for clemency. However, Gov. Perry is still able to grant a 30-day reprieve to re-examine the case.

If Buck is executed Thursday, it will be Perry’s 236th execution as governor of the state of Texas, more than any other governor in modern history.

Perry has faced criticism for his state's heavy use of capital punishment. Buck's execution will be the second of four scheduled executions in a span of eight days.

During a September 7 G.O.P. presidential debate, the Republican candidate stuck to his hard-line stance on the death penalty when he said, "In the state of Texas, if you come into our state and you kill one of our children, you kill a police officer, you're involved with another crime and you kill one of our citizens, you will face the ultimate justice in the state of Texas, and that is, you will be executed."

"There's no question about [Buck's] guilt or innocence," Hill, a native Texan said. "I'm just tired of Texas being the killingest place on the planet."